1. Technical Field of the Invention
The present invention relates generally to high frequency filters. More specifically, the present invention relates to high frequency filters in the 1 GHz to 100 GHz range that utilize patterned resonators formed on a dielectric substrate.
2. Description of Related Art
High frequency filters, such as low-pass, high-pass, band-pass, and notch filters, are very important components of modern communication systems. In particular, wireless, mobile, and optical communication systems utilize band-pass filters for isolating particular frequency channels. The frequency channels presently of interest are in a range of between 1 GHz and 100 GHz. Band-pass filters allow signals in a certain frequency band (in band frequencies) to be transmitted through the band-pass filter with minimal attenuation. The band-pass filter strongly attenuates other undesired frequencies (out of band frequencies). In the range of frequencies extending from about 1 GHz to about 100 GHz, various different types of high frequency filters have been used. The types of high frequency filters presently being used include waveguide filters, dielectric resonator filters, combline filters, microstrip filters, etc. To date waveguide filters and dielectric resonator filters have been the preferred style for obtaining high performance in the 1-100 GHz range because of their low signal attenuation in the pass band and high rejection characteristics in the out of band frequencies. Drawbacks of these waveguide and dielectric resonator filters is that they are relatively expensive, require tuning after manufacturing and are bulky in size.
Therefore, what is needed is a low cost, relatively small size filter that operates in the 1-100 GHz range that does not require tuning and has operating characteristics with low attenuation in the pass band and high rejection in the out of band frequencies.
Exemplary embodiments of the present microstrip filter operates in the 1 to 100 GHz range. Exemplary filters do not require tuning and provide relatively low loss filtering in the band pass ranges and high rejection in the out of band frequencies. Embodiments of the present inventive filter are formed on a relatively thick dielectric substrate and comprise a plurality of resonators wherein at least one of the resonators have both transverse and longitudinal gaps associated with them. Furthermore, one or more of the resonators may have a varying width over its length. In some embodiments, a xe2x80x9cdog housexe2x80x9d or tunnel like enclosure covers the resonators such that there are openings in the tunnel like cover substantially near the input and output portions of the exemplary filter. In other embodiments an enclosure covers all the resonators and there are no openings near the input and output portions of an exemplary filter. An exemplary filter provides a very low insertion loss of about 1 dB in the mid band of the filter. The filter can provide a very steep roll off xe2x80x9csteep skirtsxe2x80x9d of more than 30 dB in less than 1 GHz as the filter transitions from the pass band to the stop band. In essence the present invention provides an inexpensive, easily repeatable solution to the need for a small, low loss filter used in the GHz frequency range.